SuiteCRM switch sites, share login

In a server I have 3 identical SuiteCRM installations, with the same users/passwords.

I only changed the domain: 1: localhost/moon, 2: localhost/sun, 3: localhost/cloud.

Now I want that when a user logs in one of them they can switch to other sites without login again.

I imagine something like a combo select in each installation with the other two sites, so when the user selects another site is redirected there and logged in automatically, while the other session is destroyed.

I came from drupal and I thought to develop a custom module, but can anyone help me to start?